Narrative:

First officer's arm brushed the cannon plug carrying electricity to the R2 sliding window. A loud bang, a bright flash and lots of smoke. The first officer received a substantial burn on his right forearm. There was heavy sooting around the cannon plug and on the first officer's arm. This cannon plug was installed to facilitate the quick change of the R2 window. It is in a place where it is frequently bumped and the wire receives a great deal of flex. When maintenance examined the plug, the wires were burned through. It appears that the insulation chafed away allowing the hot wires to go to ground. There was also a butt splice connector on one of the wires inside the plug. This improperly made repair may have also contributed to the short when the first officer's arm pushed the wire to the cannon plug. This cannon plug is a company modification. I believe the window should be returned to the original boeing confign and the cannon plug should be moved to the aft side wall of the cockpit. In the interim, there should be a fleet campaign to check for frayed wires as well as to insulate and pad the point the wire flexes leaving the cannon plug. This area should then be covered with shrink wrap. Callback conversation with reporter revealed the following information: the reporter was the captain on this B737-400 and also participated in engineering discussions concerning this aircraft modification in his other role as a pilot safety representative. He said that the actual installations differed from his last understanding of the design, in that the cannon plug was supposed to be attached to a fitting against the aft wall near the circuit breaker panel to the rear of the first officer's seat with the original flexible cable running to the first officer's sliding window. Instead, the flexible cable was changed to a less, in the reporter's opinion, robust cable and it ran from the aft wall to the cannon plug which was, in turn, attached to the sliding window by another short piece of cable. The entire installation was subjected to flexing and, apparently, the cannon plug had been damaged sometime in the past, either from the flexing or from contact with persons or their equipment. This damage had been improperly repaired by using a butt splice to reconnect part of the electrical circuitry inside the cannon plug. This repair is, in the reporter's estimate, one of the possible sources of the electrical short circuit that injured the first officer. The butt splice technique was acknowledged to be incorrect by a maintenance supervisor. However, insulation was also missing from some of the flexible wiring going to the cannon plug and this was also scorched and melted. Now the entire installation is in question according to the reporter. He is unsure whether the modification met FAA, manufacturer or any formal engineering change requirements. He said the company is reviewing that process as the maintenance personnel insure that the current installations are not dangerous by inspecting the fleet and insulating all connections.

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Original NASA ASRS Text

Title: THIS ACR B737 FLC DISCOVERED A FAULT IN A MODIFICATION OF THE WINDOW HEAT WIRING SYS WHEN THE FO'S ELBOW BRUSHED AGAINST IT AND HE WAS SHOCKED AND BURNED WHEN A CANNON PLUG SHORTED. THE FO RECOVERED AND THE COMPANY IS RECHKING THESE INSTALLATIONS WHICH WERE PECULIAR TO ITS FLEET.

Narrative: FO'S ARM BRUSHED THE CANNON PLUG CARRYING ELECTRICITY TO THE R2 SLIDING WINDOW. A LOUD BANG, A BRIGHT FLASH AND LOTS OF SMOKE. THE FO RECEIVED A SUBSTANTIAL BURN ON HIS R FOREARM. THERE WAS HVY SOOTING AROUND THE CANNON PLUG AND ON THE FO'S ARM. THIS CANNON PLUG WAS INSTALLED TO FACILITATE THE QUICK CHANGE OF THE R2 WINDOW. IT IS IN A PLACE WHERE IT IS FREQUENTLY BUMPED AND THE WIRE RECEIVES A GREAT DEAL OF FLEX. WHEN MAINT EXAMINED THE PLUG, THE WIRES WERE BURNED THROUGH. IT APPEARS THAT THE INSULATION CHAFED AWAY ALLOWING THE HOT WIRES TO GO TO GND. THERE WAS ALSO A BUTT SPLICE CONNECTOR ON ONE OF THE WIRES INSIDE THE PLUG. THIS IMPROPERLY MADE REPAIR MAY HAVE ALSO CONTRIBUTED TO THE SHORT WHEN THE FO'S ARM PUSHED THE WIRE TO THE CANNON PLUG. THIS CANNON PLUG IS A COMPANY MODIFICATION. I BELIEVE THE WINDOW SHOULD BE RETURNED TO THE ORIGINAL BOEING CONFIGN AND THE CANNON PLUG SHOULD BE MOVED TO THE AFT SIDE WALL OF THE COCKPIT. IN THE INTERIM, THERE SHOULD BE A FLEET CAMPAIGN TO CHK FOR FRAYED WIRES AS WELL AS TO INSULATE AND PAD THE POINT THE WIRE FLEXES LEAVING THE CANNON PLUG. THIS AREA SHOULD THEN BE COVERED WITH SHRINK WRAP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS THE CAPT ON THIS B737-400 AND ALSO PARTICIPATED IN ENGINEERING DISCUSSIONS CONCERNING THIS ACFT MODIFICATION IN HIS OTHER ROLE AS A PLT SAFETY REPRESENTATIVE. HE SAID THAT THE ACTUAL INSTALLATIONS DIFFERED FROM HIS LAST UNDERSTANDING OF THE DESIGN, IN THAT THE CANNON PLUG WAS SUPPOSED TO BE ATTACHED TO A FITTING AGAINST THE AFT WALL NEAR THE CIRCUIT BREAKER PANEL TO THE REAR OF THE FO'S SEAT WITH THE ORIGINAL FLEXIBLE CABLE RUNNING TO THE FO'S SLIDING WINDOW. INSTEAD, THE FLEXIBLE CABLE WAS CHANGED TO A LESS, IN THE RPTR'S OPINION, ROBUST CABLE AND IT RAN FROM THE AFT WALL TO THE CANNON PLUG WHICH WAS, IN TURN, ATTACHED TO THE SLIDING WINDOW BY ANOTHER SHORT PIECE OF CABLE. THE ENTIRE INSTALLATION WAS SUBJECTED TO FLEXING AND, APPARENTLY, THE CANNON PLUG HAD BEEN DAMAGED SOMETIME IN THE PAST, EITHER FROM THE FLEXING OR FROM CONTACT WITH PERSONS OR THEIR EQUIP. THIS DAMAGE HAD BEEN IMPROPERLY REPAIRED BY USING A BUTT SPLICE TO RECONNECT PART OF THE ELECTRICAL CIRCUITRY INSIDE THE CANNON PLUG. THIS REPAIR IS, IN THE RPTR'S ESTIMATE, ONE OF THE POSSIBLE SOURCES OF THE ELECTRICAL SHORT CIRCUIT THAT INJURED THE FO. THE BUTT SPLICE TECHNIQUE WAS ACKNOWLEDGED TO BE INCORRECT BY A MAINT SUPVR. HOWEVER, INSULATION WAS ALSO MISSING FROM SOME OF THE FLEXIBLE WIRING GOING TO THE CANNON PLUG AND THIS WAS ALSO SCORCHED AND MELTED. NOW THE ENTIRE INSTALLATION IS IN QUESTION ACCORDING TO THE RPTR. HE IS UNSURE WHETHER THE MODIFICATION MET FAA, MANUFACTURER OR ANY FORMAL ENGINEERING CHANGE REQUIREMENTS. HE SAID THE COMPANY IS REVIEWING THAT PROCESS AS THE MAINT PERSONNEL INSURE THAT THE CURRENT INSTALLATIONS ARE NOT DANGEROUS BY INSPECTING THE FLEET AND INSULATING ALL CONNECTIONS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.